The present invention relates to a bipolar semiconductor device and more particularly to a bipolar power semiconductor device such as a gate turn-off thyristor (hereinafter simply referred to as a GTO thyristor) or a power transistor.
GTO thyristors and power transistors which control on-off switching of a large current by a signal applied to their control terminals contribute to reduce size and weight and promote performances of inverter devices adapted for motor control with the aim of saving energy. Because of their usefulness in this regard, production is expected to be increased drastically in the future. In particular, the GTO thyristor is designed as a large capacity device capable of handling a large amount of power. Because of this, the GTO is playing the role of a leading product in the area of large-capacity switching devices.
In order to assure efficient control of a large current, it is effective to split the emitter. Proposals have hitherto been made including an interdigital or continuous emitter structure in which interdigitally split emitters merge into a common connecting area within a semiconductor and an over-oxide emitter structure in which split finger-like emitters are electrically connected with each other by means of an electrode which overlies an oxide film. The former, however, tends to suffer from current concentration when turning off the device by a gate bias and the latter has a tendency to cause short-circuiting between the cathode and the gate.
For details of the GTO thyristor, reference may be made to U.S. Pat. No. 3,239,728, a continuation-in-part application, filed on May 27, 1981, of U.S. patent application Ser. No. 13,808 filed on Feb. 22, 1979 and assigned to the same assignee as the present application, and a continuation application, filed on June 16, 1981, of U.S. patent application Ser. No. 74,523 filed on Sept. 11, 1979 and assigned to the same assignee as the present application.